The dentate nucleus of the cerebellum projects via the superior cerebellar peduncle to the contralateral red nucleus and thalamus (VL). A lesion of the right superior cerebellar peduncle after decussation (in the midbrain tegmentum) would produce cerebellar ataxia in which limbs?

• A Right limbs ✓
• B Left limbs
• C Both limbs equally
• D No ataxia; only tremor of contralateral limbs

Explanation

The dentato-rubro-thalamo-cortical pathway crosses in the midbrain (decussation of superior cerebellar peduncle). The right dentate nucleus projects to the left thalamus via the right superior cerebellar peduncle, which crosses to the left. However, the left motor cortex then projects back down through the right corticospinal tract to control right limbs. A lesion of the right SCP after its decussation interrupts the pathway going to the left thalamus → left cortex → right limbs. Therefore, right limb ataxia results — the same side as the cerebellar lesion, due to double-crossing.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.